Is it possible to make a fish-safe mold and casting of a piece of wood? - The Planted Tank Forum
 
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post #1 of 7 (permalink) Old 03-10-2010, 02:41 AM Thread Starter
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Is it possible to make a fish-safe mold and casting of a piece of wood?

There's a beautiful chunk of root in the woods behind my boyfriend's house, with a little trimming it would be a perfect background for my 125 gallon fish tank, the only problem is, it's extremely heavy, plus i think it's probably a softwood.

My question is, would it be possible for me to make a mold and casting of this thing that would be safe to use in my aquarium? I'm assuming it's possible, but I have no experience with mold making so I don't even know where to start looking. Any advice, or links to information on this subject matter would be much appreciated.

I know I can make a foam carving, but this piece of wood I'm looking at has so much character to it, I'd really hate to use anything else.


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post #2 of 7 (permalink) Old 03-10-2010, 03:42 AM
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If it's extremely heavy, and wood, it would probably float, or be on the borderline of something that would float. Therefore you'd need to make a replica out of something just as heavy to ensure that it does not float, unless you somehow made it hollow and allowed water into it.

Make a mold out of plaster of paris or whatever. Make the replica out of plaster of paris or concrete or whatever. Paint it to color, then paint it with epoxy to make it inert (The clown puke gravel is epoxy coated to make it inert).

I think it would end up shiney, I'm not sure if steel wooling epoxy to make it matte would end up looking well.
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post #3 of 7 (permalink) Old 03-10-2010, 03:51 AM
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Another thought. Most plastics are thermoplastics. They shrink when you heat them. Say for example you cut a 2 liter bottle in half, put something in it (something slightly smaller, that will fit inside it), and hit it with a heat gun, the plastic will shrink and conform to the shape of whatever you put inside it (to some extent, 2 liter plastic will shrink to about 1/2 or 1/3rd of its size).

I would try finding a fairly rigid thermoplastic (or cut up 2 liter bottles to practice). Wrap it around or drape it over the root making sure to adhere it well so the plastic doesn't pull off, and try practicing with a heatgun. We do this all the time on a small scale for RC airplanes. Hobby shops also sell fairly large sheets of thermoplastics, I presume for similar purposes. The end result will be a hollow copy of your part. Paint the inside of the plastic, and seal it off somehow so the paint doesn't mingle with your aquarium water. You'll probably want to fill the piece with water so it will sink.

Very similar to vacuum molding. A hairdryer *MIGHT* work, I only use a heatgun however. Try at home to see if you can shrink a 2 liter with a hairdryer.
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post #4 of 7 (permalink) Old 03-10-2010, 04:16 PM Thread Starter
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Quote:
Originally Posted by sparkysko View Post
If it's extremely heavy, and wood, it would probably float, or be on the borderline of something that would float. Therefore you'd need to make a replica out of something just as heavy to ensure that it does not float, unless you somehow made it hollow and allowed water into it.
I do plan on making it hollow, open ended in back, actually, like those premade foam backgrounds. I'd like to hide most, if not all of my equipment behind it, which is why it would be nice if I was able to drill and or carve it after it's been casted, so I can put some holes in it for water intake. So, I'm thinking I'll try to go with sealed plaster of paris.

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Originally Posted by sparkysko View Post

I would try finding a fairly rigid thermoplastic (or cut up 2 liter bottles to practice). Wrap it around or drape it over the root making sure to adhere it well so the plastic doesn't pull off, and try practicing with a heatgun. We do this all the time on a small scale for RC airplanes. Hobby shops also sell fairly large sheets of thermoplastics, I presume for similar purposes. The end result will be a hollow copy of your part. Paint the inside of the plastic, and seal it off somehow so the paint doesn't mingle with your aquarium water. You'll probably want to fill the piece with water so it will sink.

Very similar to vacuum molding. A hairdryer *MIGHT* work, I only use a heatgun however. Try at home to see if you can shrink a 2 liter with a hairdryer.
Interesting idea, I think I have a hairdryer around here somewhere, I'll see if I can dig it up and give it a try, otherwise maybe I can convince someone I know to loan or give me an old hairdryer. Thanks a bunch for the suggestions : )


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post #5 of 7 (permalink) Old 03-10-2010, 06:06 PM Thread Starter
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After thinking about it a bit more, I'm thinking that plastic might be too rigid for a mold, I probably need something more flexible, because the wood has so many bumps and roots and indents.

Maybe casting rubber and some of the expanding foam I see so many people in the DIY forum using. Make a big sand pit cradle so my rubber mold doesn't lose its shape too much. It would be pretty buoyant, but if I carve away some foam and silicone it in real good, it shouldn't be any more trouble than the premade foam backgrounds.

If it's too buoyant, I'll see if I can counterweight it with some cement or something.


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post #6 of 7 (permalink) Old 03-12-2010, 05:37 AM
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Casting something that large and intricate would be incredibly time consuming and expensive. I cast a small, roughly foot-long simple log with no branches for an advanced sculpture class at school last year and it was quite a complex process.

First, I had to make a two part mold out of a flexible casting material, I believe I used a silicon mold material that runs approximately $100 a gallon. This involved coating the entire object in a specific lubricant designed for the silicon material so that the object would eventually release once the mold was made. Next, once the object is lubricated you begin to coat the entire object with a 1/16" layer of the mold material. This layer takes approximately an hour to dry. Once it is dry, you come back and coat it with another layer then let that dry. Repeating this process, you eventually create a 1/2" mold. My log took maybe an eighth of a gallon.

Before you remove the mold from the object, you have to make a mother mold out of plaster strips to support the thin silicon mold when actually pouring your replica. Without this, the silicon mold would distort or possibly break when you actually pour your material of choice into the mold. The mother mold on my log was two part, but there is really no telling how many individual sections you would need to cast a full stump, because unlike the thin silicon material which you can flip inside out and bend to get the object out of the thin mold, the plaster mother mold must slide off directly. Each larger root might take two separate sections to cast successfully. Once the mother mold has hardened, you take these sections off the object, then attempt to remove the thin silicon mold in one piece. You might need to cut a zig-zag section called a zipper into the side to allow it to come off.

Now, finally, you actually cast the object. First, you flip the mother mold upside down and craft a wooden support structure to hold the mold in place so you can pour into the open underside of the mold. Next, you slide the silicon mold into place inside the mother mold and lubricate the inside of the silicon mold. Mix together the material you have decided to cast your object out of according the directions supplied with the material, then pour it into the mold slowly so that you fill all crevices of the mold and avoid any air bubbles. Once dried, removing the mold is the same as removing it from your original object.

This is the most efficient way that I know to cast an object like a stump, but there certainly could be easier ways, as I have relatively limited casting experience.

Considering the amount of effort and funds needed to cast a stump, I would personally suggest that it would be much easier to either carve a replica out of foam or get a couple of friends to help you carry the stump to your tank.

-Mark
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post #7 of 7 (permalink) Old 03-15-2010, 10:06 AM
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Going along the final thoughts of Mark I would tend to agree with him. One could carve a replica of the stump, even if flawed, much less expensively than trying to make an exact replica mold.

In my thread, the 125 Gallon Terrarium Build (https://www.plantedtank.net/forums/vi...terrarium.html), I have a couple of links to methods and supliers of foam and expaning foam products that can be colored to almost any color one would want. These I believe would be completely safe in an aquarium. paludarium, vivarium or even as in my case a terrarium.

Best Wishes

Wes

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